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DSA_generate_parameters(3)          OpenSSL         DSA_generate_parameters(3)



NAME
       DSA_generate_parameters - generate DSA parameters

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/dsa.h>

        DSA *DSA_generate_parameters(int bits, unsigned char *seed,
                       int seed_len, int *counter_ret, unsigned long *h_ret,
                       void (*callback)(int, int, void *), void *cb_arg);

DESCRIPTION
       DSA_generate_parameters() generates primes p and q and a generator g
       for use in the DSA.

       bits is the length of the prime to be generated; the DSS allows a
       maximum of 1024 bits.

       If seed is NULL or seed_len < 20, the primes will be generated at
       random. Otherwise, the seed is used to generate them. If the given seed
       does not yield a prime q, a new random seed is chosen and placed at
       seed.

       DSA_generate_parameters() places the iteration count in *counter_ret
       and a counter used for finding a generator in *h_ret, unless these are
       NULL.

       A callback function may be used to provide feedback about the progress
       of the key generation. If callback is not NULL, it will be called as
       follows:

       o   When a candidate for q is generated, callback(0, m++, cb_arg) is
           called (m is 0 for the first candidate).

       o   When a candidate for q has passed a test by trial division,
           callback(1, -1, cb_arg) is called.  While a candidate for q is
           tested by Miller-Rabin primality tests, callback(1, i, cb_arg) is
           called in the outer loop (once for each witness that confirms that
           the candidate may be prime); i is the loop counter (starting at 0).

       o   When a prime q has been found, callback(2, 0, cb_arg) and
           callback(3, 0, cb_arg) are called.

       o   Before a candidate for p (other than the first) is generated and
           tested, callback(0, counter, cb_arg) is called.

       o   When a candidate for p has passed the test by trial division,
           callback(1, -1, cb_arg) is called.  While it is tested by the
           Miller-Rabin primality test, callback(1, i, cb_arg) is called in
           the outer loop (once for each witness that confirms that the
           candidate may be prime).  i is the loop counter (starting at 0).

       o   When p has been found, callback(2, 1, cb_arg) is called.

       o   When the generator has been found, callback(3, 1, cb_arg) is
           called.

RETURN VALUE
       DSA_generate_parameters() returns a pointer to the DSA structure, or
       NULL if the parameter generation fails. The error codes can be obtained
       by ERR_get_error(3).

BUGS
       Seed lengths > 20 are not supported.

SEE ALSO
       openssl_dsa(3), ERR_get_error(3), openssl_rand(3), DSA_free(3)

HISTORY
       DSA_generate_parameters() appeared in SSLeay 0.8. The cb_arg argument
       was added in SSLeay 0.9.0.  In versions up to OpenSSL 0.9.4,
       callback(1, ...) was called in the inner loop of the Miller-Rabin test
       whenever it reached the squaring step (the parameters to callback did
       not reveal how many witnesses had been tested); since OpenSSL 0.9.5,
       callback(1, ...) is called as in BN_is_prime(3), i.e. once for each
       witness.



1.0.1i                            2009-07-20        DSA_generate_parameters(3)